The present invention relates generally to stamp-wise cutters utilized for nibblers which are used for cutting sheets or plates of metal by punching a succession of overlapping holes along the desired contour.
More particularly, the invention relates to a cutting tool arrangement wherein a cutting head is movable with respect to a die of a nibbler.
A cutting tool assembly known for example from the Great Britain Pat. No. 1,485,795 includes a die and a one-piece cutting tool with a support shaft having a narrowing portion or neck carrying a cutting head which is periodically inserted into the die to cut off the material fed into the cutting tool. A guide ring is provided in the assembly which is positioned in a coaxial alignment with the die and connected thereto. The cutting head is guided is a direction toward the die. It has been found that although the useful life of the cutting heads in the known cutting tool assemblies permits are to use sufficiently sharp cutting edges and the neck is not broken off the shaft, the cutting tools have to be produced from a high-quality steel and to be hardened and heat-treated in a relatively expensive manner. It can not be excluded that even with many steps of heat treatment provided for the cutting heads a desirable hardness and a greater toughness may not be obtained. The cutting head which was preliminary assembled to the shaft may be broken off the shaft's neck. In order to avoid such break one tried to reduce fatigue concentrations at a transition between the shaft neck and the cutting head by provision of a smoothing zone of a relatively great radius.
This measure is normally provided preliminary and is a limited measure since the assumed difference between the diameters of the cutting head and the shaft neck may cause a so-called negative cutting angle, or in order to avoid the negative cutting angle, a larger difference between the diameters may be selected. In the first instance an undesirable impact of the cutting head against the workpiece or against the machine tool itself or both may occur in operation. One may try to counteract this disadvantage by using a considerable energy consumption during the machine operation. For this purpose a rear hub of the cutting stamps is positioned below the workpiece so that the latter and the shaft neck are pressed one opposite to the other.
During the next stroke of the stamp, the rounding between the neck and the cutting stamp pushes the workpiece and the machine apart all the more strongly.
In the second instance the disadvantage resides in that the relatively large selected difference between the diameters of the neck and the cutting head results in a greater size of the openings punched by the cutting tool which require only powerful machines to be used.